1. Field Of the Invention
The present invention relates generally to valve assemblies for transmissions and, more particularly, to a valve assembly disposed in a flow passage between a fluid reservoir and a clutch assembly in a transmission.
2. Description Of the Related Art
Transmissions are typically hydraulically operated through the use of several valves to direct and regulate the supply of fluid to frictional units. This regulated fluid supply causes either actuation or deactuation of the respective frictional units, such as clutches, for effecting gear changes in the transmission. The valves used for fluid control are typically spring loaded spool valves, spring loaded accumulators and ball check valves.
Generally, one way ball check valves are used in rotating clutches to relieve centrifugal pressure when the clutch is off and between a fluid reservoir and friction elements in transmissions. The latter type of ball check valves are located in flow passages through which positive fluid pressure flows for actuating the friction element in such a way as to allow fluid flow both through the ball seat and through a control orifice in one direction, but only through the control orifice in the opposite direction. While such ball check valves have worked well in the past, there is a need for improved shift characteristics when, for example, the transmission is shifted from underdrive to neutral. In this circumstance, fluid is dumped or vented from the clutch as it deactuates through the flow passage and past the ball check valve via the control orifice into the reservoir. If this deactuation occurs too quickly, the operator may hear and feel a "clunk" type noise as the clutch deactuates.
Further, such ball check valves may not be specifically suited to this application. Such ball check valve assemblies include castings to house the valves and these castings require much space. Thus, there is a need in the art for an improved valve assembly for use in certain flow passages in a transmission where space is very limited.